A classic in catalysis - the B.E.T. theory

N12

A Classic in Catalysis -the

B.E.T.

57(1935)1754). provided

Theory

However,

an equation

the BET paper

to calculate the area

rather than having to resort to an empirical A classic erature

is “a work,

especially

or art, of the highest

acknowledged

excellence,

in lit-

class and

method

as was necessary

the acceptance

of classics

fact, the most severe critic of the BET the-

in

catalysis but how do we define them? Like

ory, Professor

the quality of leadership,

Phys.,

classics are easy

of classic is the number

of times the work is cited. Obviously method

is not without

flaws;

some areas of science

quently than others, popular cited out of proportion

George

Halsey

16(1948)931),

of

more fre-

books will be

to scientific papers,

accepted.

isotherm are not universally

First, the theory

proposition

that Langmuir

pends on the interaction

the frequency

as, for example, we accept

Emmett,

Layers

60(1938)309).

Teller (BET)

of Gases in Multi-

(J. Am.

Chem.

Sot.,

During this period, the BET

paper was the second only Pauling’s

book,

most cited paper; “The Nature of the

Bond and the Structure of Mole-

cules and Crystals” quently.

clas-

Following

was cited more fre-

the BET paper was an-

other book, “Theory of Rate Processes” Samuel

Glasstone,

Keith J. Laidler

by and

The BET paper reasons: it provided

was notable

the surface area of a porous as an equation sorption already

to describe

data. Brunauer provided

for two

a means of calculating solid as well multilayer

ad-

and Emmett had

an empirical

method

to

the adin

in the second

layer would depend primarily on the attracmolecules

already adsorbed

in the first layer and additional

molecules

in the second

layer, and so on. But others

had developed

theories to this point. Boley

(E.C.C.

Boley,

(1937)465), generalize molecular

Proc.

for

Roy.

adsorption

tion; however,

Sot.,

example,

the Langmuir

A160

attempted treatment

to multilayer

he obtained

to

of uniadsorp-

only an empiri-

cal equation

since he could not make the

necessary

mathematical

needed for an analytical equation

depended

assumptions

solution. The BET

upon

two

assump-

tions in order to arrive at an analytical ution: (i) the heat of adsorption

sol-

in the sec-

ond and higher layers is equal to the heat of liquefaction

Henry Erying.

the de-

surface and the gas molecules

tion between If

for the period

we find a classic among

paper on “Adsorption

Chemical

sciences.

the view of citation frequency

sics: the Brunauer, molecular

by

within sub-fields

the physical

and look at this sub-field 1945-1954,

to using the

accepts adsorption

between

the first layer but adsorption

comparing

a

The theory and the equation to describe the adsorption

others, etc. Some objections

can be eliminated

that it pro-

for calculating

sorbing

frequency

(J. Chem.

admits

some fields of the literature are larger than citation

In

surface area.

this

authors

publish

of the BET equation,

vides the best method

but difficult to define.

One measure

added to

or its author”.

There has to be a number

to recognize,

for the Point B

method; this feature undoubtedly

evaporation

condensation

the molecules adsorbed

of the gases;

and (ii) the properties

in the second

of

and higher

layers are the same as those in

the liquid phase.

In the wisdom

sight, these two assumptions almost

trivial;

obtain a measure of the surface area-the

viewed

in the light of their time, and in this

Point

light, a great theoretician

B method

applied catalysis -

(J. Am.

Chem.

Sot.,

Volume 65 No. 2 -18

October

1990

however,

they

of hind-

may seem must

was needed.

be

N13

The BET theory

attracted

when it was introduced.

many critics

Most of the criti-

Columbia

University

with a B.S. degree

in

chemistry in 1929, and remained there until

cism was shown to be flawed; for example,

1942. Brunauer had come to the U.S. for a

Huttig’s

visit in 1921 following

(Monatsch.

criticism

violated

scopic

Chem., 78(1948)177) the principle

reversibility.

of micro-

A few did make im-

provements

upon the theory. For example,

the original

BET equation

the volume

adsorbed

pressure. Phys.,

McMillan

at higher J.

made

Phys.

Chem.,

modifications

mitting the heat of adsorption Brunauer

an exponential

(in E.A. Flood

(Edi-

in Budapest,

he spoke

from

Hungary.

In-

no English when he

arrived in the U.S. in 1921; eight years later he graduated

majoring

in both chemistry

and ENGLISH. Brunauer

joined

the Hun-

garian Young Workers League briefly during the mid 1920’s. Brunauer joined the US, Naval Reser-

by per-

of the various

layers to vary and obtained equation.

relative

and Teller (J. Chem.

19(1951)25);

55(1951)17)

overestimates

high school cidentally,

his graduation

ves and went on active duty in late 1942. He rose to the rank of Commander

by the

end of World War II and headed the Naval

tor),The Solid Gas Interface, Vol. 1I Marcel

research

Dekker,

pp. 77-103)

sives; he continued

of his fellow

civilian until 1951. Brunauer soon became

New

questioned

York,

1967,

the conclusions

countryman,

Teller.

a recognized

Ertl and co-workers, struments

to

in propellents

utilizing surface in-

obtain

an

independent

authority

and propellents.

and high explo-

in this position

in high explosives

The rise of McCarthyism

in the U.S. led to attacks on Brunauer and

measure of the extent of surface coverage,

his second wife, an employee

made the following

State Department,

because

17,

membership

the

as-

League,

Catalyst

Club

observations

Meeting,

1983): 1. A densely sumption

(Tri-state

November

packed monolayer

is valid. 2. A constant

adsorption

heat of

for the first layer is not valid. 3.

The assumption

that the heat of adsorption

of the second and higher multilayers same as the heat of liquefaction (although

the difference

The assumption

is not true

is not large). 4.

that the heat of adsorption

for the first layer is greater second

is the

of

of the U.S. of his earlier

Young

and he resigned

Workers

his Naval posi-

tion in June 1951. He subsequently the

Portland

Cement

another

research

joined

Association,

soon became an international area.

and

leader in yet

He finished

career as Head of the Chemistry

his

Depart-

ment and then Emeritus Professor at Clarkson University

than for the

layer is true. 5. The assumption

as a

in Potsdam,

New York.

Paul Emmett was born in Portland, Oregon in 1900. He was a high school

and

that when the first multilayer

is complete,

college

The

the higher

a statistical

odds that a small high school

in Portland,

Oregon should

at the same

coverage

multilayers distribution

have

is true. However, this

is only true for temperatures roughing

above

the

In the case of the BET equation,

the

as well as the theory, are

classics. Brunauer joined the Fixed Ni-

trogen

Laboratory,

applied

catalysis

upon graduating

-

from

Volume 65 No. 2 -18

two

physical

have enroled

who would

most-cited

sciences

defies imagination, joined

Stephen

of Linus Pauling.

time two future chemists the top

temperature.

three individuals,

classmate

the Fixed

publications

during

1926 and led a research veloped

October

1990

a mechanism

in

1945-1954

but it did happen. Nitrogen

have

Laboratory group

He in

that de-

of ammonia

syn-

N14

thesis that survives worked

even today.

for Emmett

during

period and, according

to Sir Hugh Taylor,

“These authors have given detailed

us the most

kinetic study of a single reaction,

with all aspects adsorptions,

of the reaction

studied,

kinetics, influence of reactant

concentrations,

surface

tion of composition tions

Brunauer

an eight year

areas as a func-

and mode of prepara-

The treatment

to present

complete

of the phenomenon

account

surface catalysis

by reference

example

Emmett

alone.”

an almost of

to this one

left the FNL in

1937 to head the Chemical

he worked with, among others,

Engineering

Herman

Mark, Heisenberg,

James Frank, Eucken, Donnan and Bohr. Teller came to George Washington sity in Washington, invitation

of George Gamow.

of energy

production

research area. The

had its inception

because

Brunauer

and

Brunauer

he joined the Manhattan

at Columbia

University.

In 1944,

Alamos.

a research

sion, even though

in catalytic

research.

re-

The Jahn-Tel-

University

where

Project. From Col-

umbia, he went to Chicago and then to Los

Emmett joined the Mellon Institute to head group

Washington

ler effect was another Teller classic. Teller

sity. Six years later he joined the Manhattan Project

this

a course

eventually

quested Teller’s assistance. soon went to Columbia

at the John Hopkins

during

took

that Teller offered at George University

and

the secret

in stars, and were

Univer-

Department

Gamow

unlocking

leaders in this emerging period

Univer-

D.C. in 1935 at the

Teller turned toward

BET paper

is so comprehensive

that it is possible

profession, Sommerfeld,

He became

fascinated

with fu-

Los Alamos was work-

Here he introduced

the use of isotopic

ing on atomic fission. Teller’s fascination

tracers into catalytic

research

soon became

out pioneering

research

and carried

in the Fischer-

Tropsch synthesis.

Emmett returned to the

Hopkins

in 1955 as W.R. Grace

University

Professor.

He retired in 1971 but remained

active as Research State University

Professor

at Portland

until his death in 1985. One

the H-bomb

reality with the explosion in October

In the case of the BET theory, theory and the three scientists tined to become

vives

during the height of the energy crisis in the

all three remain leaders.

However,

publications

in the history of catalysis,

of

B.H. DAVIS

for funding!!

even today, one can select any

of Emmett’s

However,

a proposal

to study the surface area and porosity coal, and it was not approved

has not been

Of the scientist, only Teller sur-

of the ironies of research funding was that, late 1970’s, Emmett submitted

both the were des-

classics. The theory, now

after more that 50 years, surpassed.

of

1952.

New Environmental

Centre

and read a clas-

sic: one that is exceptionally

well written,

that pushes the interpretation

of the data

New challenges tween

lie ahead

of us be-

now and the end of the twentieth

to, but never over, the limit, and a paper

century as we attempt to deal with emerg-

that is as scientifically

ing environmental

issues. Some of these

require immediate

attention so that we can

valid today as when

it was written. Edward

Teller was born in Budapest,

Hungary in 1908. Throughout was associated

his career he

with scientists

of excep-

tional ability. In just his preparation

applied

catalysis

-Volume

meet the increasingly tions on a relatively

are global scale problems

for his

65 No. 2 -18

demanding

October

1990

regula-

local basis, and there that urge long-